In recent years, as one of effective measures against globally-concerned global warming, particular attention is given to a carbon dioxide capture and storage technique for capturing and storing a carbon dioxide gas contained in an exhaust gas. As an example of the technique, a carbon dioxide separation and capture apparatus has been considered, which causes an absorbing liquid to absorb carbon dioxide gas contained in combustion exhaust gas discharged from a thermal power plant or the like or carbon dioxide gas contained in process exhaust gas, separates the carbon dioxide gas from the exhaust gas, and captures the carbon dioxide gas.
The carbon dioxide separation and capture apparatus includes an absorption tower and a regeneration tower, for example. The absorption tower is configured to cause an absorbing liquid to absorb carbon dioxide gas contained in supplied exhaust gas and generate a rich liquid. The regeneration tower is configured to cause the rich liquid supplied from the absorption tower to release the carbon dioxide gas and generate a lean liquid. The lean liquid generated by the regeneration tower is supplied to the absorption tower, and the rich liquid is generated from the lean liquid. A heat exchanger, installed between the absorption tower and the regeneration tower, is configured to cause thermal exchange between the rich liquid to be supplied to the regeneration tower from the absorption tower and the lean liquid to be supplied to the absorption tower from the regeneration tower. The rich liquid supplied to the regeneration tower is heated by a steam generated by a reboiler from the absorbing liquid and then releases the carbon dioxide gas. The carbon dioxide gas released from the rich liquid is discharged from the regeneration tower. In this manner, the carbon dioxide separation and capture apparatus separates the carbon dioxide gas from the exhaust gas and captures the carbon dioxide.
The amount of the carbon dioxide gas captured by the carbon dioxide separation and capture apparatus is expressed by a product of an average amount of the carbon dioxide gas contained in the exhaust gas and an average rate of capturing the carbon dioxide gas. In a thermal power plant, a flow rate of exhaust gas or the concentration of carbon dioxide gas in the exhaust gas vary due to power control, a generation load, a method of operating a boiler, or other factors. The rate of capturing carbon dioxide can therefore fluctuate as well.
A partial capture method of capturing a predetermined amount of carbon dioxide even if a flow rate of exhaust gas or the concentration of carbon dioxide gas fluctuate has been considered.
However, if the amount of carbon dioxide gas to be captured is maintained at a predetermined target amount and energy required to capture the carbon dioxide gas increases, effectiveness in the measures against global warming can decrease.